Sugar surfactants such as, for example, alkyl polyglycosides or fatty acid-N-alkyl glucamides, are distinguished from other surfactants by their excellent detergent properties and high ecotoxicological compatibility. For this reason, these classes of nonionic surfactants are acquiring increasing significance. They are generally used in liquid formulations, for example, dishwashing detergents and hair shampoos.
While conventional sugar surfactants perform satisfactorily in many applications, there is a constant need to both enhance and expand their performance properties. Methods of improving the performance of conventional sugar surfactants by increasing their: foaming and foam stability, tolerance to water hardness and detergency, continue to be sought.
A specific problem associated with sugar surfactants, and particularly alkyl polyglycosides, relates to the undesirable formation of complex ion precipitates during both the production of the alkyl polyglycosides, and during their end-use in wash waters (laundry, dish washing, etc.) due to the presence of hard water metal ions in the process waters.
Alkyl polyglycosides are glucose ethers wherein the anomeric alcohol group is replaced by an alkoxy group. Some of the glucose moieties are oligomerized such that a typical alkyl polyglycoside sample is comprised of a mixture of isomeric monoglycosides, diglycosides, triglycosides, etc., with each higher oligomer present in decreasing amounts. Alkyl polyglycosides have an average degree of oligomerization (DP) of from 1.4 to 1.7 units of glucose. Alkyl polyglycosides are conveniently prepared by reacting an alcohol of the type and chain length which is desired to form the "alkyl" portion of the glycoside of interest with a saccharide reactant (e.g., a monosaccharide such as glucose, xylose, arabinose, galactose, fructose, etc., or a polysaccharide such as starch, hemicellulose, lactose, maltose, melibiose, etc.) or with a glycoside starting material wherein the aglycone portion thereof is different from the alkyl substituent desired for the ultimate alkyl glycoside product of interest. Typically, such reaction is carried out under conditions wherein the alcohol is present in a mole ratio of alcohol/glucose in the range of from 2.0 to 5.0, at an elevated temperature and in the presence of an acid catalyst. The product contains alkyl polyglycoside and excess alcohol which is normally removed by distilling the alcohol from the alkyl polyglycoside product. Because the alcohol distillation operation requires temperatures in excess of 150.degree. C., thermal degradation of the alkyl polyglycoside normally takes place and produces an undesirable color in the product. The alcohol-free alkyl polyglycoside product is then normally subjected to one or more decolorization operations wherein the product is reacted with hydrogen peroxide or a Group I or Group II metal borohydride to remove any color bodies which may have been formed during the prior process steps such as the alcohol removal operation. In the event that hydrogen peroxide is used to bleach the alkyl polyglycoside product, magnesium oxide is typically used as a peroxide stabilizer. Consequently, the bleached alkyl glycoside product contains anywhere from 300 to 500 ppm of magnesium.
When formulating an alkaline cleaning composition, silicates are often employed as builders due to their favorable cost and performance. The incorporation of silicates into cleaning compositions containing alkyl polyglycosides as nonionic sugar surfactants results in the formation of an undesirable magnesium silicate precipitate due to the presence of magnesium ions present in both the alkyl polyglycoside product and process waters. Metal ion precipitates may also be formed during the washing of an article of manufacture wherein hard water ions are present in the wash water. Consequently, the elimination of hard water ion precipitates in wash liquors is also desirable.